Long travel hydraulic cushion device



1965 w. H. PETERSON LONG TRAVEL HYDRAULIC CUSHION DEVICE 4 Sheets-Sheet 1 Filed Nov. 29, 1965 \w 47 mm mm mhl 7 4 /7 QM M l I \w @i mm\m\ mm 52 km INVENTOR WILL/AM H. PETERSON Dec. 21, 1965 w. H. PETERSON 3,224,599

LONG TRAVEL HYDRAULIC CUSHION DEVICE 4 Sheets-Sheet 2 Filed Nov. 29, 1963 INVENTOR W/LL/AM H. PETERSON 4 Sheets-Sheet 5 INVENTOR. WILL/AM H. PETERSON w km R k 9 H. PETERSON LONG TRAVEL HYDRAULIC CUSHION DEVICE Dec. 21, 1965 Filed Nov. 29, 1963 Dec. 21, 1965 w. H. PETERSON 4 Sheets-Shee Filed Nov. 29, 1963 6% i INVENT 1gV/LL/A/ H PETERSON United States Patent 3,224,599 TRAVEL HYDRAULKC CUSHION DEVEQE William H. Peterson, Homewood, ill, assignor to iuiiman Incorporated, Chicago, Ill., a corporation of Delaware Filed Nov. 29, 1963, Ser. No. 326,971 5 Claims. (Cl. 213-43) The present invention relates to cushion devices, and more particularly to a hydraulic cushion device which is employed in railway vehicles constructed such that the coupler carrying structure and the lading supporting structure are lengthwise movable relatively to each other upon impact at the couplers and the hydraulic cushion device is disposed for interaction between the aforementioned structures to absorb a portion of the impact energy to prevent lading damage.

The hydraulic cushion device to which the present invention relates comprises generally a hydraulic fluid filled cylinder and a fluid displacement means. The cylinder and fluid displacement means are arranged to reciprocate relative to each other from a neutral extended position to a contracted position upon impact to either one or the cylinder or fluid displacement means. Upon relative movement of the cylinder and fluid displacement means to the contracted position the fluid displacement means is operative to displace fluid from a high pressure chamber to a low pressure chamber in a manner which results in absorbing a portion of the kinetic energy of the impact force.

Associated with the cylinder and fluid displacement means to provide an additional low pressure chamber volume is an expandable boot. In the neutral or extended position of the fluid displacement means and the cylinder the expandable boot is deflated and upon impact the volume of fluid received within the low pressure chamber causes the boot to expand to receive the predetermined volume of displaced fluid.

Also associated with the hydraulic cushion device is a return spring means which is disposed between the fluid displacement means and the cylinder so as to be operative to return the aforementioned components from the contracted to the neutral position after the force of impact has been dissipated. During the return travel to the neutral position the flow of the displaced fluid is reversed to flow from the low pressure chamber to the high pressure chamber such that the flexible boot reservoir is again deflated.

The above described cushion device is generally installed between the relatively movable coupler carrying structure and the lading supporting structure for interaction therebetween so that the cushion device is operative to absorb a portion of the impact force on the couplers. The amount of energy transmitted to the lading supporting structure is maintained at a level which does not result in damage to the lading carried on the 0 lading carrying structure.

Railway vehicles having relatively lengthwise movable coupler carrying and lading supporting structure may be ot the cushion underframe type employing a coupler carrying sliding sill which is movable lengthwise of the underirame, or may be of the type employing a lading supporting rack-like component mounted for relative lengthwise movement on the underframe which carries the couplers. In both of the vehicle structures generally described above, interaction between the coupler carrying and lading supporting structures is achieved by two sets of stop arrangements of which one set is fixed to the coupler carrying structure and the other set is fixed to the lading supporting structure.

Each of the two sets of stops include spaced stop members, one stop arranged to be engaged with opposite ends of the cushion device in the extended or neutral position thereof. Upon impact to either one of the couplers the stop member fixed to the coupler carrying structure on the side of impacted coupler is operative to contract the cushion device against the opposing one of stop members fixed to the lading supporting structure. In this manner the cushion device is rendered operative to absorb a portion of the kinetic energy of the impact force so that the remaining portion transmitted to the lading supporting structure is below that causing damage to the lading carried thereon.

After the impact force is dissipated, the return spring means, acting between the fluid displacement means and the cylinder, returns the cushion device to its neutral extended position. At the same time the stop member on the coupler carrying structure which, initiated by the contraction of the cushion device, is also urged to its normal or neutral position by the extending end so that the two sets of the lading support stops and coupler carrying structure stops are both engageable with the opposing ends of the cushion device. As above described, during the return movement the fluid flow is reversed such that the flexible boot is deflated.

The above described operation of the cushion device occurs upon impact in one direction and in the absence of an impact on the opposite end prior to the return of the cushion device to the neutral position. Should, however, an impact be applied in the opposite direction prior to the time that the cushion device reaches its neutral position, the impact on the opposite coupler causes the coupler carrying stop means to rapidly reverse their directions such that the return spring force is not resisted and the cushion device also tends to extend more rapidly. This requires that the flow of the fluid from the boot reservoir and low pressure chambers be accomplished so that the volume of the displaced fluid therein be decreased at rate commensurate with the reduction of the decreasing volume of the flexible boot reservoir and returned to occupy the volume in the high pressure chamher which is provided therefor in the neutral position of the cushion unit. Should the hydraulic flow not be sufficiently rapid, the flexible boot tends to expand and stretch to provide the required volume for the fluid retained therein and a portion of the high pressure chamber may be only partially filled so as to create a vacuum therein. Under these conditions, should another impact be applied to the couplers while the flexible boot is thus partially inflated and stretched and the high pressure chamber within the cylinder is under vacuum, the cushion device will not provide an adequate force resisting the impact blow, and additional hydraulic fluid which may be as great as that displaced upon the initial impact of the sequence of impact is again introduced into the flexible boot reservoir. This tends to further expand and stretch the flexible boot beyond its original capacity. Such stretching and expansion of the boot interferes with the operation of the cushion device and under some circumstances may even cause rupturing of the flexible boot.

It is the principal object of the present invention to provide a cushion device of the above generally described type with means for overcoming the difliculties encountered heretofore.

It is a further object to provide a cushion device of the above described general type having a cylinder, a fluid displacement means reciprocable therein and defining a high pressure chamber and a low pressure chamber within the cylinder, and a flexible boot chamber communicating with the low pressure chamber with an arrangement for assuring that the return flow of the hydraulic fluid from the flexible boot reservoir and the low pressure chamber to the high pressure chamber in the presence of a rapid sequence of oppositely applied forces is adequate to prevent excessive stretching and expansion of the expandable boot and the creation of a vacuum within the high pressure chamber.

It is a further object to provide a hydraulic cushion device of the type employed in cushion railway car construction having a hydraulic fluid filled cylinder within which there is reciprocable a fluid displacement means which upon contractions from a neutral position is operative to displace fluid from a high pressure chamber and a low pressure chamber, and flexible boot chamber for receiving a portion of displaced hydraulic fluid with an arrangement disposed on the high pressure side of the fluid displacement which is responsive to a preselected pressure in the low pressure chamber to provide additional return flow volume between the low and high pressure chambers.

In the drawings:

FIG. 1 is a fragmentary cross-sectional view of a hydraulic cushion device embodying the present invention in the extended or neutral position thereof.

FIG. 2 is a fragmentary cross-sectional view similar to FIG. 1 but showing the cushion device in the contracted position assumed upon impact.

FIG. 3 is an enlarged fragmentary cross-sectional view of the cylinder and the fluid displacement means with the latter embodying the reverse flow arrangement of the present invention.

FIG. 4 is a front elevational view similar to FIG. 3.

FIGS. 5, 6 and 7 are diagrammatic illustrations of the hydraulic cushion unit incorporating the reverse flow or hydraulic fluid flow balancing arrangement showing in particular the reverse flow path of the hydraulic fluid as the hydraulic cushion unit travels from contracted position shown in FIG. 5 and intermediate and fully extended positions shown in FIGS. 6 and 7 respectively.

FIG. 8 is a fragmentary cross-sectional view of a piston head disposed in the cylinder of a cushioning device showing the piston head provided with another form of reverse flow arrangement.

FIG. 9 is a sectional view taken generally along the lines 99 of FIG. 8.

Referring now to the drawings there is shown a hydraulic cushion unit 19 comprising essentially a hydraulic fluid filled cylinder 11, a fluid displacement means 12 which is reciprocable within the cylinder 11 from a neutral to a contracted position for displacing fluid from a high pressure chamber 13 to a low pressure chamber 14, a flexible boot reservoir 16 connected between the cylinder 11 and fluid displacement means 12 providing a selected volume for receiving a portion of the hydraulic fluid displaced during contraction, a metering pin 17 for metering the flow between the high pressure and low pressure chambers 13 and 14 and a return spring means 18 for returning the fluid displacement means 12 and the cylinder 11 to the neutral position after the shock of impact causing the contraction has been dissipated.

In accordance with the present invention, the cushion device is provided with a high speed return or reverse flow arrangement which is disposed on the fluid displacement means 12 between the high pressure chamber 13 and the low pressure chamber 14 so as to be operative upon preselected pressure forces within the low pressure during the return travel to provide an adequate return flow of the hydraulic fluid from the flexible boot reservoir and the low pressure chamber to the high pressure.

As shown in FIGS. 1 to 4, the cylinder 11 is formed from a cylindrical tube 21 made from steel or the like. Fixed as by welding to one end of the tube 21 is a base or follower plate 22 which extends beyond the outer circumference of the tube 21 to provide return spring retaining ledge 23. Fixed within cylinder bore 24 inwardly of open end thereof is an intermediate cylinder head 26 defining adjacent the open end a boot chamber 27 for accommodating the flexible boot 16.

As shown, the length of the boot chamber 27 may be enlarged so as to provide an annular shoulder 28 against which a peripheral flange 30 on the intermediate cylinder head is held fixed by way of a snap ring 29. The snap ring 29 abuts against a retainer ring 31 fixed to a midportion of the intermediate cylinder head 26. Disposed between the retainer ring 31 and the peripheral flange 30 is a slidable compression ring 32 which is urged against an O-ring 33 to compress the latter to form a fluid-tight seal along the wall of the bore by a plurality of radial spaced clip members 34. For a more detailed description of the sealing arrangement reference is made to US. patent application Serial Number 244,410, filed Dec. 13, 1962, assigned to the assignee of the present invention. The intermediate cylinder head 26 as shown also includes an axial opening 36 and a boss 37 about which there is fastened one end of the flexible boot reservoir 16.

The fluid displacement means 12 includes a piston head 33 to which there is fixed one end of a tubular piston rod 39 which extends outwardly of the open end of the cylinder through the axial opening 36 of the intermediate cylinder head 26 to define therewith an annular opening 41. The piston head 38 defines on one side thereof with the cylinder head 22 the high pressure chamber 13 and on the opposite side thereof with the intermediate cylinder head 26 and flexible boot reservoir 16 the low pressure chamber 14.

The piston head 38 may be formed from a suitable metal such as cast iron and the circumference thereof is slightly spaced from the inner wall of the cylinder bore 24. Seated within a peripheral groove 42 is a sealing and guiding ring 43 which is preferably formed from laminated phenolic resin. The sealing and guiding ring 43 is sized so as to form a sliding seal at the inner wall of the cylinder bore 24.

As shown, the forward or leading face of the piston is formed with a circular recess 44 having a substantially planar annular bottom face 46 from which there extends a rearwardly directed frustrum of a cone feed surface 47. The feed surface 47 merges with a rim 48 about an axial orifice 49 formed in the piston head 38.

The tubular piston rod 39, as shown, is formed from a hollow tubular rod having a bore 51 which is coaxial with the piston head orifice 49. Fixed to the end of the piston rod remote from the piston head 38 is a second base plate 52. The base plate 52 may be attached as shown to the shank 53 of a fastening member 54 having an externally threaded head 56 which is screwed into the internally threaded end of the piston rod 39. Disposed within the piston rod bore 51 inwardly of the fastening member 54 there may be a suitable charging check valve assembly 57 for charging fluid into the device 10. In the event the check valve is employed the hydraulic fluid is charged therethrough prior to fastening the base plate 52 on the piston rod 39.

The flexible boot 16 may be formed from a suitable flexible and resilient material which is fluid impervious, as, for example, rubber. The boot 16 is connected at one end to the boss 37 of the intermediate cylinder head 26 as by a hose clamp. At the other end the boot is reversely turned and the reversed end is clamped to the piston rod 39 also by means of a hose clamp. As shown in FIG. 1 in the extended or neutral position of the hydraulic cushion device 10 the boot 16 is deflated and substantially devoid of fluid, but in the contracted position it is expected and inflated by a portion of the fluid displaced during contraction of the unit 10 as more fully to be explained hereinafter. It is to be noted, however, that the volume of displaced hydraulic fluid received Within the boot 16 is such that the latter is not expanded to an extent greater than the volume of the boot chamber 27.

Fastened to the base plate 22 and coaxially extending through the piston head orifice into the piston rod bore is the metering pin 17 which serves to control the fiow from the high pressure chamber 13 to the low pressure chamber 14. Preferably the flow between the high and low pressure chambers is such as to impart approximately constant force travel characteristics to the cushion unit during contraction thereof. To this end, lengthwise extending flutes 58 are formed along the periphery of the metering pin to vary the effective area of orifice 49 through which the fluid flows during the contraction. The flutes 58 are formed to cooperate with the piston head orifice 49 to maintain the pressure forces within the high pressure chamber 13 approximately constant upon relative movement of the piston head 38 with respect to the cylinder 11 by varying the effective orifice area at the rim 48 in accordance with the total cross-sectional area of the flutes 58 encompassed by the rim 48. In this connection it is to be noted that the total effective cross-setcional area is at the maximum in the extended position and gradually decreases to a minimum at the end of the contraction to cut off any substantial flow between the high and low pressure chambers 13 and 14.

Limiting the extended length of the cushion device 10 is a top ring 61 which is fixed as by welding to the outer circumference of the piston rod 39. The stop ring 61 may be formed with an inclined face which in the extended position of the unit abuts against a complementary inclined face formed on the inner face of the intermediate cylinder head 26.

To provide communication between the piston rod bore 51 and the low pressure chamber 14 the piston rod 39 includes an array of ports 62 located adjacent to the piston head 38. Thus communication and flow of the hydraulic fluid between the low pressure chamber 14 and high pressure chamber 13 is established via the piston head orifice 49 and the flutes 58, the piston rod bore 51, and ports 62.

Disposed between the base plates 22 and 52 is the return spring means 18 which serves to return the cylinder 11 and the fluid displacement means 12 from the contracted position assumed upon impact to the normal or neutral extended position shown in FIG. 1. The return spring means may include a plurality of springs 18a and 18 arranged in tandem.

As shown in FIG. 2 in the compressed position of the cushion unit 10, the metering pin.17 is located relative to the piston head such that substantially all flow is cut off through the flutes 58 and the orifice 49. Thus, during return of the piston head 38 and the cylinder to the neutral position, the flow of hydraulic fluid gradually increases as the effective orifice area, which as previously explained is defined by the depths of the flutes 58 and the orifice rim 48, increases. Under some circumstances of railway car operation, such as when sequential rapid and oppositely directed impact forces are applied to the cushion unit lit), the return of the cylinder 11 and piston head 38 is accomplished within a short period and much more rapidly than the hydraulic fluid may flow through the gradually increasing effective orifice area to maintain the high pressure chamber 14 filled. Under these circumstances the volume of fluid within the combined volume of the low pressure chamber 14 and the flexible boot 16 is in excess of that for which the unit is designed and the volume of fluid within the high pressure chamber is less than the design volume. Thus the increased volume of fluid within the low pressure chamber and the flexible boot 16 causes the latter to be radially and longitudinally expanded beyond the confines of the boot chamber 27. This excessive expansion of the boot 16 may result in rupturing of the flexible boot 16 or tearing of the latter by the spring upon further relative contraction of the cylinder and piston.

Moreover, the absence of sufiicient hydraulic fluid within the high pressure chamber 13 to fill the latter creates a vacuum therein such that if an impact is applied to the unit at this time the resisting force or energy absorbing capacity will be far below the design capacity of the unit. At the same time the hydraulic fluid would be displaced into the low pressure chamber 14 and the flexible boot 16 so as to further expand the latter.

In accordance with the present invention there is provided a hydraulic fluid volume balance or reverse flow arrangement which serves to maintain the hydraulic fluid volume within the flexible boot 16 and the low pressure chamber 14 at a level below that causing expansion of the boot 16 outwardly of the confines of the boot chamber 27 and maintains the volume within the high pressure chamber 13 filled.

As shown in the embodiment of FIGS. 3-4, this may be accomplished by the provision of a fluid pressure responsive arrangement which is operative upon inadequate flow of hydraulic fluid through the effective orifice area during the return stroke of the cushion device 10 to provide an increased hydraulic fluid flow which maintains the proper fluid volume balance. To this end the piston head 38 is formed with a plurality of angularly spaced orifices 64. Seated within the circular recess formed on the high pressure chamber face of the piston head 38 and overlying the orifices or openings 64 is an annular valve member 66. The valve member 66 may include an annular metal disc.

Normally urging the valve member 66 into seating engagement are a plurality of spring fingers 67 which are attached to the face 65 of the piston head 38 by a retaining ring 63. Screws 69 fasten the ring and springs to the piston head 38.

FIGS. 8 and 9 illustrate a further embodiment of a hydraulic fluid balancing arrangement formed on the piston head. Seated within the piston head recess 44 is the annular valve disc 66. The valve disc 66 is loosely disposed within the recess 44 for movement from a position superposed over the openings 64 to a position spaced therefrom as shown in the phantom line position of FIG. 8. Limiting outward movement of the annular disc 66 outwardly of the openings 64 is a snap ring 6% which is inserted in a groove 71 formed along the wall 73 of the recess 44.

During the compression stroke as when the cushion device is traveling to the contracted position, the valve disc 66 is pressed into sealing engagement on the face 46 over the openings 64 by the pressure forces of the fluid acting thereon. During the return travel the pressure forces within the low pressure chamber 14 and acting on the annular valve disc 66 through the openings 64, are operative to displace the disc 66 from the superposed position and against the stop ring 69 so that hydraulic fluid freely flows through the openings 64.

In operation the cushion device it) of the present invention is disposed for interaction between the sliding sill 71 and a stationary sill 72 of a cushion underframe railway car as schematically illustrated in FIGS. 5 to 7. When thus disposed, in the neutral position of the cushion device 10, the base plates are engaged by respective stationary sill cushion stops 7474 fixed to the stationary sill and with the sliding sill stops 76-76 fixed for movement with the sliding sill 71 of which the latter carries the couplers (not shown.)

Assuming an impact at the right end of the sliding sill 71, the force of the impact causes the sliding sill to move toward the left relative to the stationary sill 72 as shown in FIGS. 5 and 6. The movement of the sliding sill '71 causes the right ones of the sliding sill stops 7676 movable therewith and engaging the base plate 22, to compress the cushion device against the opposing left ones of the stationary sill stops 7474.

During compression or contraction of the cushion unit 10 the piston head 38 and base plate 22 move toward each other whereupon the metering pin 17 fixed to the latter displaces hydraulic fluid within the piston rod bore 51 outwardly through the array of ports 62 into the low pressure chamber 14 and the flexible boot reservoir 16 via the annular opening 41.

At the same time fluid displaced from the high pressure chamber 13 flows through the gradually decreasing orifice area at the orifice 49 into the piston rod bore 51 and into the low pressure chamber 14 via the array of ports 62 and the flexible boot via the annular passage 41.

The hydraulic fluid is discharged into the low pressure chamber 14 at a high velocity which creates a considerable turbulence. The turbulence is caused, at least in part, by the radially directed flow of hydraulic fluid impinging directly against the inner wall of the cylinder 11 so as to dissipate much of the kinetic energy of the impact in the form of heat.

When the cushion device has completed its travel the cushion device is fully compressed and the metering pin 17 and piston head 38 are located relatively to each other such that the latter lies somewhat beyond the ends of the flutes 58. In this position of the piston head 38 and the metering pin 17 substantially no flow occurs through the orifice 49.

Normally, in the absence of a shock impact on the opposite end, the return spring means 18 acting between the base plates 22 and 52 is operative to extend the cushion device whereupon the base plate engaging the right sliding sill stop 76 is operative to also return the sliding sill 71 to the neutral position shown in FIG. 7. During the return movement of the cushion unit to the neutral position as shown in FIG. 6 the flow of the hydraulic fluid is reversed such that the cushion unit is again in position to be operative to perform its energy absorbing function. The return travel of the cushion unit 10 to the neutral position under the influence of the spring 18 alone generally occurs over a period of time which permits the hydraulic fluid to flow through the gradually increasing effective orifice area at a rate which maintains the pressure forces within the low pressure chamber 14 and the flexible reservoir tube 16 at a minimum and maintains the gradually increasing volume of the high pressure chamber 13 substantially filled with hydraulic fluid. Thus the flexible reservoir tube is not subjected to any substantial expansion beyond the boot chamber 27 and substantially no vacuum is created within the high pressure chamber 14.

Assuming the reverse flow arrangement of FIGS. 1-4 is employed, in the absence of a substantial increase of the hydraulic fluid pressure forces in the low pressure chamber the annular valve member 66, which is exposed to these forces via the orifices 64, remains in seating engagement under the influence of the spring fingers 67 and the pressure forces of the fluid within the high pressure chamber 13.

However, should the return period of the cushion unit 10 from the compressed to extended positions be materially increased, the effective orifice area at the piston orifice 49 may not be adequate to permit the hydraulic fluid to flow therethrough at a return rate which is adequate to maintain the high pressure chamber 13 fully charged and excessive hydraulic fluid may remain within the low pressure chamber 14 and the flexible boot 16. The excessive hydraulic fluid within the low pressure chamber 14 and the flexible boot 16 creates a corresponding increase in the pressure forces within these components which, in the absence of any means for relieving the same, tends to cause extreme expansion of the flexible boot 16.

The above conditions are accentuated when an impact force is applied at the left in the same direction in which the sliding sill 71 is moving before any substantial return movement of the cushion unit 10 occurs. The sliding sill is thus moved to the right whereby the left sliding sill stop 76 is out of engagement with the base plate as shown in FIG. 6. Thus, the sliding sill 71 no longer offer any resistance to the force of the return spring 18 so that the piston head 38 and cylinder 11 move more rapidly to the neutral position. This rapid movement of the piston head 38 and the cylinder 11 does not permit adequate flow through the restricted piston head orifice 49 so that the excessive volume of hydraulic fluid within the low pressure chamber 14 creates pressure forces which are applied on the inner face of the annular valve member 66. When the pressure forces are such that the opposing force of the spring fingers 67 retaining the annular valve member 66 is overcome, the latter is displaced out of seating engagement over the orifices 64 such that hydraulic fluid is free to flow therethrough into the high pressure chamber 14. Preferably the force of the spring fingers is adjusted to yield under hydraulic fluid pressure forces which are less than those causing substantial expansion of the flexible boot 16 outwardly of the confines of the boot chamber 27. In this manner the hydraulic fluid pressure forces on the flexible boot 16 are maintained below those tending to cause excessive expansion thereof.

Assuming now that the reverse flow arrangement of FIGS. 8 and 9 is employed, it should be readily apparent that as soon as the return travel is initiated the pressure forces of the hydraulic forces within the low pressure chamber 14 will displace the annular valve member 66 to the phantom line position shown in FIG. 8.

Upon returning to the neutral position and during the return travel, the high pressure chamber 13 is substantially completely filled with hydraulic fluid. Thus, in the event that an impact shock is applied prior to or immediately after the device is in the neutral position shown in FIG. 7 the filled volume of the high pressure chamber 13 is available to resist the force of the impact. When the pressure forces within the low pressure chamber are reduced to a lesser magnitude than the force of the spring fingers, the valve member 66 again seats over the orifice 64 to close off the flow of hydraulic fluid therethrough.

What is claimed is:

1. A hydraulic cushion device comprising a cylinder having a bore, a first cylinder head fixed to one end of said cylinder, an intermediate cylinder head fixed Within said cylinder bore inwardly of the other end thereof, an axial opening .in said intermediate cylinder head, a piston head disposed within said cylinder bore and defining a high pressure chamber on one side thereof with said first cylinder head and a low pressure chamber on the opposite side thereof, for movement between said intermediate cylinder head and said first cylinder head, an axial orifice formed in said piston head, a tubular piston rod fixed at one end to said piston head and extending through said axial opening, stop means on said piston rod engageable with said intermediate cylinder head for maintaining said piston head at a minimum spacing adjacent sad intermediate cylinder head, port means formed in said tubular piston rod between said stop means and said piston head and constantly communicating with said low pressure chamber, a flexible boot reservoir connected between said intermediate cylinder head and said piston rod and extending toward the remaining end of said cylinder, a second cylinder head fastened to the other end of said tubular piston rod, fluid passage means .in said intermediate piston head to provide fluid communication between said low pressure chamber cylinder bore and said flexible boot reservoir, a metering pin fixed to said first cylinder head and extending through said piston head orifice and into said bore of said tubular piston rod to provide a gradually diminishing flow area through said orifice when said piston head moves toward said first cylinder head, hydraulic fluid filling said cylinder and said piston rod bore, a plurality of angularly spaced openings formed in said piston radially outwardly of said piston head orifice, and an annular plate means supported on the side of said piston head facing said first cylinder head, said annular plate means being movable from a position covering said plurality of openings upon movement of said piston head from a position adjacent said intermediate cylinder head to a position adjacent said first cylinder head, and a position spaced from said openings when said piston head returns to said position adjacent said intermediate cylinder head.

2. The invention as defined in claim 1 including spring means urging said annular plate member covering said openings during movement toward said first cylinder head, said spring means being yieldable under the pressure forces of the hydraulic fluid in the low pressure chamber during return to said position adjacent said intermediate cylinder head.

3. The invention as defined in claim 1 wherein said annular plate member is disposed in a recess formed on said piston head side facing said first cylinder head.

4. The invention as defined in claim 3 wherein a stop ring is disposed Within said recess for limiting outward movement of said annular plate member.

5. The invention as defined in claim 2 wherein said spring means comprises a plurality of angularly spaced spring fingers fixed to said head and yieldably engaging said annular plate member.

References Cited by the Examiner ARTHUR L. LA POINT, Primary Examiner.

EUGENE G. BOTZ, Examiner.

B. FAUST, Assistant Examiner. 

1. A HYDRAULIC CUSHION DEVICE COMPRISING A CYLINDER HAVING A BORE, A FIRST CYLINDER HEAD FIXED TO ONE END OF SAID CYLINDER, AN INTERMEDIATE CYLINDER HEAD FIXED WITHIN SAID CYLINDER BORE INWARDLY OF THE OTHER END THEREOF, AN AXIAL OPENING IN SAID INTERMEDIATE CYLINDER HEAD, A PISTON HEAD DISPOSED WITHIN SAID CYLINDER BORE AND DEFINING A HIGH PRESSURE CHAMBER ON ONE SIDE THEREOF WITH SAID FIRST CYLINDER HEAD AND A LOW PRESSURE CHAMBER ON THE OPPOSITE SIDE THEREOF, FOR MOVEMENT BETWEEN SAID INTERMEDIATE CYLINDER HEAD AND SAID FIRST CYLINDER HEAD, AN AXIAL ORIFICE FORMED IN SAID PISTON HEAD, A TUBULAR PISTON ROD FIXED AT ONE END TO SAID PISTON HEAD AND EXTENDING THROUGH SAID AXIAL OPENING, STOP MEANS ON SAID PISTON ROD ENGAGEABLE WITH SAID INTERMEDIATE CYLINDER HEAD FOR MAINTAINING SAID PISTON HEAD AT A MINIMUM SPACING ADJACENT SAID AINTERMEDIATE CYLINDER HEAD, PORT MEANS FORMED IN SAID TUBULAR PISTON ROD BETWEEN SAID STOP MEANS AND SAID PISTON HEAD AND CONSTANTLY COMMUNICATING WITH SAID LOW PRESSURE CHAMBER, A FLEXIBLE BOOT RESERVOIR CONNECTED BETWEEN SAID INTERMEDIATE CYLINDER HEAD AND SAID PISTON ROD AND EXTENDING TOWARD THE REMAINING END OF SAID CYLINDER, A SECOND CYLINDER HEAD FASTENED TO THE OTHER END OF SAID TUBULAR PISTON ROD, FLUID PASSAGE MEANS IN SAID INTERMEDIATE PISTON HEAD TO PROVIDE FLUID COMMUNICATION BETWEEN SAID LOW PRESSURE CHAMBER CYLINDER BORE AND SAID FLEXIBLE BOOT RESERVOIR, A METERING PIN FIXED TO SAID FIRST CYLINDER HEAD AND EXTENDING THROUGH SAID PISTON HEAD ORIFICE AND INTO SAID BORE OF SAID TUBULAR PISTON ROD TO PROVIDE A GRADUALLY DIMINISHING FLOW AREA THROUGH SAID ORIFICE WHEN SAID PISTON HEAD MOVES TOWARD SAID FIRST CYLINDER HEAD, HYDRAULIC FLUID FILLING SAID CYLINDER AND SAID PISTON ROD BORE, A PLURALITY OF ANGULARLY SPACED OPENINGS FORMED IN SAID PISTON RADIALLY OUTWARDLY OF SAID PISTON HEAD ORIFICE, AND AN ANNULAR PLATE MEANS SUPPORTED ON THE SIDE OF SAID PISTON HEAD FACING SAID FIRST CYLINDER HEAD SAID ANNULAR PLATE MEANS BEING MOVABLE FROM A POSITION COVERING SAID PLURALITY OF OPENINGS UPON MOVEMENT OF SAID PISTON HEAD FROM A POSITION ADJACENT SAID INTERMEDIATE CYLINDER HEAD TO A POSITION ADJACENT SAID FIRST CYLINDER HEAD, AND A POSITION SPACED FROM SAID OPENINGS WHEN SAID PISTON HEAD RETURNS TO SAID POSITION ADJACENT SAID INTERMEDIATE CYLINDER HEAD. 